When a colored plastic composition for molding, fiber, film or sheet is prepared, a so-called masterbatch or color concentrate is often prepared first. The masterbatch or color concentrate is usually composed of a pigment composition containing high concentration of pigment mixed with a plastic, and is later diluted with a plastic, which can be the same as or different from the one present in the masterbatch or color concentrate, to form a plastic composition for molding, fiber, film or sheet, which is then made into final form (such as molded to obtain a molded article, through spinnerets to form fibers, form films and sheets, or to form a composition for a coating).
When a pigment composition is mixed with a thermoplastic polymer to prepare a masterbatch, color concentrate, color compound, or a plastic composition for molding, fibers, films, or sheets, the pigment often forms large aggregates or agglomerates which tend to clog the screens in the fiber spinning heads, form un-dispersed pigment color specks on molded parts and other equipment, form un-dispersed pigment specks in films and sheets, resulting either in broken filaments, changing fiber spinning screen packs frequently and shutting down of the whole fiber processing line, or producing off spec molded articles, off spec films with poor properties, and off spec sheets, etc. Moreover, with increased viscosity, productivity (i.e., the number of molded articles, length of fiber, and surface area of film/sheet, per unit of time) tends to drop rather drastically. When this happens, the whole system has to be stopped to remove the aggregates in order to either reduce the filter pressure and regain the efficient fiber operation speed or in order to eliminate pigment color specks for molded articles, films, and sheets. Such interruptions cause inefficiency and increased cost and difficulty.
Several methods are available to improve the dispersibility of the pigment. U.S. Pat. No. 6,013,126 discloses salt grinding organic pigments, then kneading with alkanoic acids to improve dispersibility in plastics.
JP11130974 discloses preparation of organic pigments by dissolving in an aprotic solvent (DMSO) in the presence of a base (NaOH) and water or a C1-C4 alcohol, and then quickly precipitating the pigment particles by addition to water, alcohol and/or an acid (H2SO4).
U.S. Pat. No. 5,900,050 discloses treating organic pigments with quaternary ammonium compounds or amines to give pigments with good dispersibility in plastics.